Rabies in Texas
Eric Fonken, DVM, MPAff; Zoonosis Control Branch; Texas Department of State Health Services
Laura E. Robinson, DVM, MS; Director, Oral Rabies Vaccination Program, Zoonosis Control Branch, Department of State Health Services
Rabies is a virus that can infect the central nervous system of warm-blooded animals, including humans. Worldwide it kills thousands of people annually, mostly in Africa and Asia, with dogs being the primary source of transmission. In the United States, the canine strain of rabies has been eliminated through the use of effective animal vaccines, the widespread adoption of mandatory vaccinations for dogs and cats, and effective animal control laws, among other strategies.
Wildlife, particularly high risk species such as bats, skunks, raccoons, coyotes, and foxes, continue to be a source of rabies infection for domestic animals and humans in Texas. In the mid-1990s, the Department of State Health Services (DSHS) Zoonosis Control Branch (ZCB) initiated successful oral rabies vaccination programs (ORVP) targeting large outbreaks of rabies in foxes in west and west-central Texas and coyotes in south Texas. Today, an ORVP for foxes and coyotes is maintained along the Texas-Mexico border. In the last decade, skunks and bats have been the primary reservoirs for rabies in Texas, and a study evaluating ORV in skunks was initiated in east-central Texas in 2012.
Since the 1980’s, domestically acquired human rabies cases have most commonly resulted from exposure to rabid bats. It has been estimated that in general, about 1% of bats in the wild are infected with the rabies virus, although the risk of infection increases dramatically among sick or downed bats. On average, 10% of the bats submitted for rabies testing in Texas are infected. Most species of bats have very small teeth and a minor bite or scratch may go unnoticed, leaving the victim unaware that they may have been exposed to rabies.
Texas law requires that all potential rabies exposures (bites, scratches, or other potential exposures) to humans or domestic animals be reported to the Local Rabies Control Authority (LRCA) and that the exposing animal, if available, be either quarantined and observed (10 days for healthy dogs, cats and ferrets; 30 days for most other domestic animals), or euthanized and tested for rabies at a public health laboratory. State law also requires that all dogs and cats in Texas be vaccinated against rabies by 16 weeks of age. Effective vaccines are available for other species of domestic animals.
Rabies virus is present in the saliva of a rabid animal and is primarily transmitted via a bite, although fresh open wounds and mucous membranes are other potential routes of exposure. Avoiding direct physical contact with wildlife, particularly high risk species, is key to preventing rabies in domestic animals and humans. Animal bites or scratches potentially contaminated by saliva should be immediately and thoroughly washed soap and water and an iodine-based antiseptic (if not contraindicated due to allergy) should also be applied to the wound(s).
If a person is potentially exposed to rabies, the development of clinical disease may be prevented by the timely administration of post-exposure prophylaxis (PEP), which consists of the administration of human rabies immune globulin (HRIG) and 4 doses of vaccine over a period of 2 weeks. If PEP is not administered or not administered in a timely manner, clinical rabies may develop, resulting in death in almost all cases.
The clinical course of rabies in humans and animals is divided into three stages: an asymptomatic incubation period, overt clinical illness, and death. The incubation period is highly variable and depends on a number of factors, including the amount and strain of virus inoculated, the location of the bite, the type of animal infected, and the age and immune status of the victim. Typically, the incubation period in humans lasts one to three months, although it can be as short as 1 week or longer than 1 year in rare instances. Once clinical illness becomes apparent, the disease is rapidly progressive in both animals and humans. The saliva, cerebrospinal fluid and nervous tissue of a clinically ill human or animal are considered infectious for rabies.
Initial symptoms of rabies in humans often include fever, pain or altered sensations at the wound site, headache, and malaise. As the disease progresses, more overt and progressive neurologic symptoms develop and can include limb weakness or paralysis, behavior changes, hallucinations, insomnia, hydrophobia (abnormal fear of water) and/or aerophobia (abnormal fear of air flow), seizures, and coma, followed in almost all cases by death.
In animals, the first symptoms of rabies may be nonspecific and include lethargy, fever, vomiting, and anorexia. Signs progress within days to cerebral dysfunction, cranial nerve dysfunction, ataxia, weakness, paralysis, seizures, difficulty breathing, difficulty swallowing, excessive salivation, abnormal behavior, aggression, and/or self-mutilation, followed by death.
Humans exposed to rabies should receive timely PEP. Domestic animals exposed to rabies must either be euthanized or undergo PEP, if a licensed vaccine is available for that species, and isolated for a specified period of time, depending on the vaccination status of the animal at the time of the exposure. ZCB personnel are available for consultation related to potential rabies exposures, including exposure risk assessment, LRCA contact information, PEP recommendations, and sources of rabies vaccine and HRIG for medical providers. To locate the Regional ZCB office for your area, please see the map on the DSHS website at http://www.dshs.state.tx.us/idcu/health/zoonosis/contact/. Additional information about rabies and other zoonotic diseases in Texas may be found at http://www.dshs.state.tx.us/idcu/health/zoonosis/.